1. Field of the Invention
The invention relates to improved methods and apparatus for servicing wells with coiled tubing and coiled tubing components comprised of composite fiber materials. In a preferred embodiment, fiber reinforced coiled tubing, provided as a layered laminate, is used within a wellbore to provide a strong and versatile coiled tubing for wellbore operations. In one embodiment, signals representing data may be transmitted along the length of the coiled tubing to the surface, providing useful information used in monitoring and directing coiled tubing operations. Further, composite disconnects are disclosed for disconnection of coiled tubing from tool strings facilitating retrieval of the coiled tubing from the wellbore.
Using this invention it is possible to vary the section modulus along the length of coiled tubing to improve buckling characteristics. Using intrinsic fibers for data communication is also part of this invention.
2. Description of the Prior Art
Coiled tubing is increasing in popularity as a method of conducting operations in an oil or gas wellbore. Historically, drilling pipe was used for drilling and conducting operations inside a wellbore, usually several hundred or thousand feet under the surface of the ground. However, drill pipe must be assembled in sections and lowered into the wellbore over a long time period of many hours or days. Coiled tubing emerged as a solution by providing a relatively fast and reliable method of conducting operations downhole within a wellbore, without using heavy and cumbersome jointed drilling pipe. Coiled tubing is used as a continuous strand, and therefore is easier and faster to use in many wellbore operations. Technological developments, improved service reliability, and the need to drive down industry costs have contributed to expanded uses for coiled tubing.
Modern coiled tubing operations are used to drill slim hole wells (wellbores of smaller than normal diameter), deploy reeled completions, log high angle boreholes, and deploy treatment fluids downhole. The use of coiled tubing in horizontal wellbores (i.e. wellbores that deviate from vertical) is increasing at a rapid rate.
In some instances, well treatment fluids are pumped downhole through the interior hollow space of the coiled tubing, and then are made available to the subterranean formation.
One of the primary limiting factors in coiled tubing workover applications, particularly in horizontal wells, is the depth to which coiled tubing can be pushed without locking or buckling in the production tubing, casing or open hole. The usefulness of coiled tubing is greatly limited by its inability to proceed farther into horizontal wells without buckling or locking within the wellbore. Coiled tubing is not rotated, but instead is pushed into and out of the wellbore. The frictional forces of the coiled tubing rubbing against the interior of the wellbore eventually overcome the integrity of the coiled tubing, causing buckling and lock up of the tubing in the wellbore. This phenomenon is illustrated in FIG. 4.
Another limiting factor that prevents the use of coiled tubing in deeper wells is the internal strength of the coiled tubing itself. Coiled tubing, when suspended in a wellbore, is subjected to the pull of gravity. Since a length of coiled tubing weighs several thousand pounds, the coiled tubing must have enough internal integrity and strength to withstand this force during operations without separating into two or more pieces. This problem is compounded when additional weight (such as drilling or completion apparatus) is placed on the distal end of the coiled tubing and lowered into the wellbore. Further, if the coiled tubing is restricted due to frictional forces or "hangs" within the wellbore, the additional force necessary to pull the coiled tubing free is added to the weight forces, thereby working to undesirably separate the coiled tubing at its weakest point.
Another criteria for coiled tubing is that it must be capable of being spooled onto a reel for storage, and for transport to the well site. Coiled tubing reels are deployed from trucks for land based wells, and from ships for servicing offshore wells. The most practical way to handle relatively long lengths of coiled tubing is to spool the tubing upon a reel. However, spooling a length of coiled tubing onto a reel subjects the tubing to bending forces that can damage the coiled tubing, and sometimes make it difficult to properly store and deploy the tubing.
The design of coiled tubing is complicated by the fact that the tubing must show sufficient strength to conduct the coiled tubing operations downhole without failure or buckling, while at the same time being flexible enough to be spooled onto a reel after the operation is complete. Unfortunately, coiled tubing that has a high section modulus and is therefore advantageous as to its strength and buckling characteristics downhole is difficult to spool onto a reel. The properties that make tubing work well downhole (i.e. stiffness) also work to disadvantage on the surface of the ground when attempting to spool the tubing.
What has been needed in the industry for some time is a coiled tubing that is stronger and more resistant to the forces encountered within a wellbore, but at the same time is easily spoolable, facilitating tubing operations in deeper wells. A coiled tubing that can be used in deeper wells, and also is capable of extended reach into horizontal wells is needed.
One additional problem encountered in coiled tubing operations is that the amount of real time information available to a coiled tubing operator during coiled tubing operations currently is very limited. A need exists for a reliable method and apparatus for sending signals from the lower portion of the wellbore to the surface. Signals could be converted to data that is used, for example, to monitor the properties of the coiled tubing, events outside and/or inside any length or a particular length of coiled tubing or to monitor the operation of downhole tools mounted upon the distal end of the coiled tubing. In some cases of pumping fluids through the coiled tubing, an apparatus could be used to monitor the leakage from the tubing, or perhaps monitor the integrity of the coiled tubing. This apparatus would be integral to the composite coiled tubing.
In many instances, it is very important to know reliably the exact depth of the coiled tubing in the wellbore, or in some instances, the exact point in the formation that corresponds to the downhole tool or other apparatus mounted on the end of the coiled tubing. There is needed a method or apparatus by which a coiled tubing operator may operate coiled tubing in a manner to know exactly (or within very narrow limits) the location of the tubing in relationship to the subterranean formation for use in isolating zones, providing diverting fluids, etc. to a specific portion of the reservoir.
Another significant problem in coiled tubing operations is the method and apparatus for disconnection of coiled tubing from tool strings during coiled tubing operations. Typically, either mechanical or hydraulic disconnects have been used in coiled tubing applications. However, there are problems with mechanical and hydraulic disconnects.
The disconnects, which are run above the tool string, facilitate release of the tool string by the tubing in the event the tool string becomes lodged in the hole. The alternative would normally result in tensile failure of the tubing close to the well head (near the surface of the ground at the reel end of the tubing), thereby complicating tubing retrieval. A disconnect may also be desirable at a length from the distal end for allowing the lower length to be left in the hole. Thus disconnecting the tool string from the tubing is necessary in many instances.
If is difficult to predict exactly at what load mechanical disconnects will fail. This is because such disconnects typically use a small number of studs or screws that are designed to fail at a pre-set load. A problem with such mechanical disconnects is that the failure load range is fairly broad due to the indefinite tolerances of the failure mechanism.
What is needed in the industry is a disconnect that will fail at a relatively narrow range or exact load rating. Predictability in failure load, and failure at a narrow load range, is desirable. Further, a disconnect that can be activated on demand would be desirable, because it would eliminate the uncertainty associated with known methods of disconnection, and would permit an operator to disconnect on demand.